1. Field of the Invention
The present invention relates to a wall plug for securing a fixing, such as a screw, to a wall.
In particular, the present invention relates to a wall plug assembly which enables the wall plug to be inserted into a wall without requiring the separate pre-drilling of an accommodating bore.
2. Description of the Related Art
‘Self-tapping’ wall plugs are known; for example see EP 0557292 and EP 0425358. Both EP 0557292 and 0425358 disclose a wall plug having an external screw thread which secures the plug axially within the wall once the plug has been fully inserted. The plug has a central through bore which axially accepts a blade-like drilling tool which protrudes axially beyond the terminal end of the wall plug.
In use, the blade-like tool is mounted in the chuck of a drill and a wall plug is axially slid onto the tool.
The terminal end of the tool is then presented to the surface of the wall into which the plug is to be inserted.
The tool is rotated by the drill and as it axially advances into the wall it drills out a pilot bore. When the terminal end of the wall plug reaches the pilot bore, it enters into the bore and the external threads on the wall plug bite into the bore walls to cause the wall plug to be axially advanced into the bore to its fully inserted position by a screwing action. Accordingly, with this type of wall plug, drilling of a pilot bore and insertion of the wall plug is conveniently carried out in one operation.
A problem with this type of arrangement is that initial entry of the terminal end of the wall plug into the pilot bore may prove difficult due to the screw threads on the wall plug failing to bite into the pilot bore and also due to the transition between the blade-like tool and the terminal end of the wall plug. This problem may result in the destruction of the screw-threads and/or an undesirable widening of the pilot bore entrance.